I am writing my detailed experience so that you can appropriately weigh in my comments and put them in contex.
I have owned 5 LS cars - 90, 95, 98, 2001, 2007. The 90 was in a league of its own - far ahead of its competition - I put 250,000 miles on it and kept it for 9 years or so. I did not like the 95 better (less solid than 90). Transmission was apparently made lighter. There was nothing wrong with a 95 but it was really the same (less?) car. The 98 was quite an improvement over the 95 - quicker too. My first Nav and it worked fine. The 2001 was really not a major improvement. At the same time period, I had owned a Merc s class AMG. The 430 was quicker in city and convenient to drive. the s class was felt a bit heavy in city driving but was simply superb on the highway. the ls 430 was simply not in the same league beyond 75 mph. But the merc engine and transmission felt a lot less refined than the lexus'.
Recently, I test drove the S550. It felt more like my old ls 430 (quiet and a slightly floaty ride! - it almost felt that merc was following lexus!).
I did test drive the standard 460L but I really don't remember how it felt. Mine is the touring/sport version - with 19" tires, bigger brakes, air suspension. My 95 had air suspension but I really did not find it to be superior. My 98 and 2001 did not have air suspension. But this 2007's air suspension is clearly superior to my 95's.
I do agree with you that the steering feel is really not too different from previous cars (actually even the 90 felt pretty much the same). If you really want the best steering feel - you should drive Audi A8! Between LS 460, S550 and A8, The A8 has the best steering feel and fun factor of driving. I was less impressed with S500 - Obviously it too is quite good of course - I preferred my ls 460.
Besides the steering feel, the 460L is, in my opinion, a clearly desirable car and the 430 should be a quick trade in. Considering your preference for steering feel, you should buy the sport/touring version (available by special order) and use it in sport setting. Granted, it would not drive like an A8 or a 750il. Assuming that monetary factor is not an issue, I would encourage you to trade in your 430 for a sport 460L. You will be quite pleased. Perhaps your local dealer has a sport version demo? They are not very common. In fact, my local dealer asked me to do him a favor and let one of his customers drive it (which I obliged and that person immediately ordered the sport package). There is one issue with the touring version you have to understand - its tires and brakes will have half the life of the normal car. I do not know whether it stops shorter or better but I am pleased. I really don't mind changing the tires/brakes. After all, lexus is low maintenance anyway!